Anticorrosion primer coating composition

ABSTRACT

The present invention relates to an anticorrosion primer coating composition comprising (i) a polyvinyl butyral resin, (ii) an organo functional silane, (iii) at least one member selected from the group consisting of inorganic borate compounds and polyphosphate compounds, and (iv) phosphoric acid.

BACKGROUND OF THE INVENTION

(1) Field of the Invention:

The present invention relates to an anticorrosion primer coatingcomposition for metals of the type generally called a "wash primer","shop primer", "etch primer" or "prefabrication primer". Moreparticularly, the invention relates to an anticorrosion primer coatingcomposition for metals which comprises as indispensable components (i) apolyvinyl butyral resin, (ii) an organo functional silane, (iii) atleast one member selected from the group consisting of borate compoundsand polyphosphate compounds and (iv) phosphoric acid and which mayfurther comprise a phenolic resin and/or a metal powder according toneed.

(2) Description of the Prior Art:

Steel frames and metal sheets or plates for steel structures such asships and bridges have heretofore been ordinarily coated withanticorrosion primer coating paints, that is, shop primers, aftercomplete removal of rust and mill scales by sand blasting so as toprevent rusting during processing or fabrication.

For example, D. A. Bayliss et al. proposed and examined variousprefabrication primers (shop primers) in the Journal of the Oil andColour Chemists' Association, 51, pages 792-915 (1968) published by theOil and Colour Chemists' Association.

Shop primers include wash primers for which the conversion treatment isconducted simultaneously with the coating operation, namely shop primerscalled "shop primers of the conversion treatment type".

A typical composition for such wash primer comprises a polyvinyl butyralresin as a vehicle, phosphoric acid, chromic anhydride, zinc chromateand an alcohol.

The above-mentioned wash primer is produced in two types: a wash primerof the etching type and a wash primer of the high exposure resistancetype.

The wash primer of the etching type is suitable for the preliminarytreatment of metals to be coated and is prepared by dissolving apolyvinyl butyral resin in an alcohol, kneading and grinding a zincchromate pigment with the resulting solution and adding an additivecontaining phosphoric acid to the thus prepared main composition. Ingeneral, wash primers of this type are used when top coating is effectedwithin a short time from the primer coating and are applied so as toimprove adherence between a metal substrate and a top coating layer. Inother words, it is not such a strict requirement for single layers ofwash primers of the etching type to have high corrosion resistance as itfor wash primers of the high exposure resistance type.

As the wash primer of the etching type, there has long been known acomposition comprising a polyvinyl butyral resin, phosphoric acid andzinc tetraoxychromate (see the specification of U.S. Pat. No.2,525,107). There is also known a composition comprising a modifiedvinyl resin obtained by reacting chromium trioxide and phosphoric acidwith a vinyl resin and basic zinc chromate (see the specification ofU.S. Pat. No. 2,488,651).

The wash primer of the latter type, namely the wash primer of the highexposure resistance type, comprises a main composition comprising apolyvinyl butyral resin and a phenolic resin as a vehicle and a zincchromate pigment kneaded and ground with the vehicle and an additiveincluding an alcohol solution of phosphoric acid. In general, the maincomposition is mixed with the additive at the time of application andthe resulting coating composition is applied to form a coating layerexcellent in adhesion to a metal substrate and to a top coat paint.Since the wash primer of this type is used when top coating is appliedafter the lapse of a long time from formation of the primer coating, thewash primer of this type is required to have such a corrosion resistancethat the primer coating is resistant to exposure for at least about 6months.

A typical composition for such wash primer of the high exposureresistance type is disclosed in the specification of U.S. Pat. No.3,791,850.

In the art, wash primers of the high exposure resistance type haveheretofore been mainly used as shop primers.

As will be apparent from the foregoing, conventional wash primersinclude a zinc chromate pigment or chromic anhydride. Therefore, theyentail a problem of chromium pollution. Namely, workers breathe in spraydust formed in the coating step and their health is impaired by chromiumions contained in such spray dust.

This chromium pollution is now a serious social problem, and developmentof an anti-pollution wash primer has been eagerly desired in the art.

For example, attempts have heretofore been made to replace zinc chromatepigments by other anti-pollution pigments. However, coatings formed fromwash primers containing such pigments are defective in the corrosionresistance and adhesion. Thus, no practical anti-pollution wash primerhas yet been developed in the art.

For example, although an anticorrosion primer paint comprising apolyvinyl butyral resin, zinc chromate and barium metaborate isdisclosed in Japanese Patent Public Discloure No. 44322/73, in thisprimer paint only a part of the zinc chromate is replaced by bariummetaborate and the hygienic problem of prevention of harmful pollutionis not completely solved. Further, as is taught in this publiclydisclosed specification, a coating from a a primer comprising apolyvinyl butyral resin and barium metaborate alone is extremely poor incorrosion resistance and though this wash primer is free of chromium anddoes not cause a pollution problem, it cannot be used practically.

Further, a paint composition comprising an oil varnish, oil-modifiedalkyd resin or drying oil as a vehicle and barium borate is known in theart (see the specification of U.S. Pat. No. 2,818,344), but thiscomposition only provides a film having improved mold resistance orchalk resistance and has few properties required of a wash primer.

Still further, the specifications of U.S. Pat. Nos. 3,272,663 and No.3,528,860 teach that a molybdate compound is used as an anticorrosionpigment for the wash primer. However, paints of this type are stillinsufficient in corrosion resistance.

Moreover, an attempt has been made to replace a zinc chromate pigment bya phosphate, for example, zinc phosphate (see the above-mentioned D. A.Bayliss et al. reference). Furthermore, a flame or corrosion resistantpaint comprising a white pigment such as silicon phosphate, zirconiumphosphate, zinc phosphate or titanium phosphate and an alkyd resin,epoxy resin air-drying oil, phenolic resin, polyvinyl acetate resin,vinyl chloride resin or polyvinyl acetal resin is known in the art (seethe specification of U.S. Pat. No. 3,892,577). These paints, however,have few of the properties required of a wash primer.

As one kind of shop primer, there is known a so-called zinc rich primerformed by incorporating zinc dust at a high concentration in a vehicle.Although this primer has a very high corrosion resistance, it has afatal defect of poor weldability. Namely, when a steel material coatedwith this primer is subjected to the welding operation, blow holes areformed by a gas generated from the primer coating and the weld strengthis drastically reduced. Furthermore, fumes of zinc generated at the stepof welding of the primer-coated material has serious influences on thehealth of workers and the problem of maintenance of good healthconditions is left unsolved.

From a different view point, a so-called electroprint marking process inwhich an image is directly formed and developed on a coated steel plateaccording to the electroprint process has recently been adopted in theship-building industry so as to save labor.

In this case, a paint excellent in both electric conductivity andcorrosion resistance is ordinarily applied to a steel plate, and a washprimer to which electric conductivity has been imparted is especiallyused for formation of such electrically conductive corrosion-resistantcoating. Development of a wash primer free of chromium and capable ofeliminating safety and health problems has also been desired in thisfield where a wash primer is utilized in the electroprint markingprocess.

As will be apparent from the foregoing, shop primers excellent incorrosion resistance, adhesion to a top coating or over-coating(over-coatability), weldability, adaptability to the electroprintmarking process and operation safety (freedom from environmental andhygienic problems at various operation steps) have not yet beendeveloped in the art.

The present invention has now been achieved as a result of our researchwork made with a view to developing primer coating compositions whichovercome the foregoing defects involved in conventional coatingcompositions.

SUMMARY OF THE INVENTION

The present invention relates to a novel anticorrosion primer coatingcomposition.

It is a primary object of the present invention to provide ananticorrosion primer coating composition which does not causeenvironmental pollution, especially chromium pollution.

Another important object of the present invention is to provide ananticorrosion primer coating composition capable of providing a coatingexcellent in physical and chemical properties such as corrosionresistance, weldability, adaptability to weld cutting, adherence and thelike.

Still another object of the present invention is to provide ananticorrosion primer coating composition excellent in adaptability tothe electroprint marking process.

More specifically, in accordance with the present invention, there isprovided an anticorrosion primer coating composition of the etching typecomprising (i) a polyvinyl butyral resin, (ii) an organo functionalsilane, (iii) at least one member selected from the group consisting ofborate compounds and polyphosphate compounds and (iv) phosphoric acid.In accordance with the present invention, there also is provided ananticorrosion primer coating composition of the high exposure resistancetype formed by incorporating a phenolic resin into the above primercoating composition of the etching type. Further, in accordance with thepresent invention, there is provided an anticorrosion primer coatingcomposition having good adaptability to the electroprint markingprocess, which is formed by adding a metal powder to the above-mentionedanticorrosion primer coating composition of the etching type or highexposure resistance type.

DETAILED DESCRIPTION OF THE INVENTION

Commercially available polyvinyl butyral resins having an average degreeof polymerization of about 500 to about 1000 and a degree of butyrationof about 57 to about 70 mole % can be directly used as the polyvinylbutyral resin (i) in the present invention.

As the organo functional silane (ii) that can be used in the presentinvention, there can be mentioned, for example, aminoalkoxysilanesrepresented by the following formula: ##STR1## wherein R¹ stands for adivalent hydrocarbon group having 1 to 4 carbon atoms, R² and R³represent a monovalent hydrocarbon group having 1 to 4 carbon atoms, Zstands for a hydrogen atom or an aminoalkyl group, and m is 1 or 0(zero), and alkylalkoxysilanes represented by the following formula:##STR2## wherein R⁴ stands for a divalent hydrocarbon group having 1 to4 carbon atoms, R⁵ and R⁶ represent a monovalent hydrocarbon grouphaving 1 to 4 carbon atoms, Q stands for a methacryloxy, acryloxy,glycidoxy or epoxycyclohexyl group, and n is 1 or 0 (zero).

As typical instances of the compounds represented by the general formula(1), there can be mentioned aminomethyltriethoxysilane,N-(β-aminoethyl)-aminomethyltrimethoxysilane, aminomethyldiethoxysilane,N-(aminoethyl)-aminomethyltributoxysilane, γ-aminopropyltriethoxysilane,γ-aminopropylmethyldiethoxysilane, γ-aminoisobutyltrimethoxysilane,N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane andN-(β-aminoethyl)-γ-aminopropylmethyldimethoxysilane.

As typical instances of the compound represented by the general formula(2), there can be mentioned γ-glycidoxypropyltrimethoxysilane,γ-glycidoxypropylmethyldimethoxysilane,β-(3,4-epoxycyclohexyl)-ethyltrimethoxysilane,β-(3,4-epoxycyclohexyl)-ethyltriethoxysilane,β-(3,4-epoxycyclohexyl)-ethylmethyldimethoxysilane andγ-methacryloxypropyltrimethoxysilane.

Further, organo functional silanes containing a vinyl group, such asvinyltriethoxysilane and vinyl-tris-β-methoxyethoxysilane, can be usedas the component (ii) in the present invention.

The foregoing organo functional silanes can be used singly or they maybe used in the form of a mixture of two or more of them.

Among the foregoing organo functional silanes, alkoxysilane compoundsrepresented by the formula (2) are preferably employed, and use ofβ-(3,4-epoxycyclohexyl)-ethyltrimethoxysilane,γ-glycidoxypropyltrimethoxysilane and--methacryloxypropyltrimethoxysilane is especially preferred.

As the borate compound that can be used as component (iii) in thepresent invention, there can be mentioned, for example, zinc borate(2ZnO.3B₂ O₃.3.5H₂ O), barium borate (BaB₂ O₄.H₂ O), calcium borate(CaO.B₂ O₃.5H₂ O), potassium tetraborate (K₂ B₄ O₇ .5H₂ O), calciumtetraborate CaB₄ O₇.6H₂ O), sodium tetraborate (Na₂ B₄ O₇) bariumtetraborate (BaB₄ O₇), manganese tetraborate (MnB₄ O₇.8H₂ O), zinctetraborate (ZnB₄ O₇), lithium tetraborate (Li₂ B₄ O₇), magnesiummetaborate (Mg₂ B₂ O₄.8H₂ O) and aluminum orthoborate (Al₂ O₃.B₂ O₃).These borates may be used singly or in the form of a mixture of two ormore of them. Use of zinc borate and/or barium borate is especiallypreferred.

As the polyphosphate compound that can be used as other type of thecomponent (iii) in the present invention, there can be mentionedcompounds obtained by reacting phosphoric acid with a di- to hexa-valentmetal or its oxide or hydroxide (presented as "X") at a P₂ O₅ /X molarratio in the range of from 1 to 6 under heating to effect condensation.

As the reactant X, there can be mentioned, for example, metals such asMg, Al, Ca, Zn, Mn, Fe and Ba, oxides such as MgO, Al₂ O₃, CaO, ZnO,MnO₂, FeO, MoO₃, BaO and WO₃, and hydroxides such as Mg(OH)₂, Al(OH)₃,Ca(OH)₂, Zn(OH)₂, Ba(OH)₂ and Fe(OH)₃.

These polyphosphate compounds can be used singly or in the form of amixture of two or more of them. Use of zinc polyphosphate, aluminumpolyphosphate, calcium polyphosphate and mixtures of two or more of themis especially preferred. Commercially available aluminum polyphosphateK-50, K-80 and K-82 (trademarks for products manufactured by TeikokuKako Co., Ltd.) and HB Hardener (trademark for the product Hoechst AG)are conveniently used in the present invention.

Phosphoric acid that is used as component (iv) in the present inventionis an acid formed by hydration of diphosphorus pentoxide.

More specifically, there can be mentioned metaphosphoric acid,pyrophosphoric acid, orthophosphoric acid, triphosphoric acid,tetraphosphoric acid and the like. These phosphoric acids may be usedsingly or in the form of a mixture of two or more of them.

Any of metal powders capable of imparting an electric conductivity tothe resulting coatings can be used as the metal powder in the presentinvention. Ordinary metal powders having a size of about 500 to about180 mesh can be used in the present invention. More specifically, in thepresent invention there can be used aluminum powder and powders ofalloys of aluminum with at least one metal selected from the groupconsisting of zinc, magnesium, tin, silicon, copper and manganese. Useof aluminum powder is especially preferred.

In the present invention, these metal powders can be used singly or inthe form of a mixture of two or more of them.

The anticorrosion primer coating composition according to anotherembodiment of the present invention further comprises a phenolic resin.Commercially available phenolic resins for paints can be directly usedfor this embodiment of the present invention. These phenolic resins areordinarily formed by condensing a phenol with an aldehyde according to acustomary method and they have an average molecular weight of about 100to about 1000.

In the present invention, good results are obtained when 100 parts byweight of a polyvinyl butyral resin is mixed with 20 to 350 parts byweight, preferably 50 to 250 parts by weight, of at least one memberselected from the group consisting of borate compounds and polyphosphatecompounds, 1 to 25 parts by weight, preferably 3 to 15 parts by weight,of an organo functional silane and 5 to 50 parts by weight, preferably15 to 40 parts by weight, of phosphoric acid.

When using a mixture of a borate compound and polyphosphate compound,the mixing weight ratio of borate compound and polyphosphate compound isfrom 9/1 to 1/9, preferably from 8/2 to 4/6.

When the amount of the mixture of the borate compound and polyphosphatecompound or the amount of the organo functional silane is outside theabove-mentioned range, reduction of the corrosion resistance isobserved.

In this embodiment of the present invention using a phenolic resin, itis preferred that up to 200 parts by weight, especially 70 to 170 partsby weight, of the phenolic resin be incorporated in 100 parts by weightof the polyvinyl butyral resin. When the amount of the phenolic resinexceeds 200 parts by weight per 100 parts by weight of the polyvinylbutyral resin, the adhesion to the top coating or over-coating(over-coatability) is reduced.

When a metal powder is incorporated in the anticorrosion primer coatingcomposition of the present invention, the metal powder is used in anamount of 10 to 130 parts by weight, preferably 15 to 90 parts byweight, per 100 parts by weight of the polyvinyl butyral resin. When theamount of the metal powder is smaller than 10 parts by weight per 100parts by weight of the polyvinyl butyral resin, the adaptability to theelectroprint marking process is degraded, and when the amount of themetal powder is larger than 130 parts by weight per 100 parts by weightof the polyvinyl butyral resin, the corrosion resistance or adhesiontends to decrease.

The coating composition of the present invention comprises asindispensable components (i) a polyvinyl butyral resin, (ii) an organofunctional silane, (iii) at least one member selected from the groupconsisting of borate compounds and polyphosphate compounds and (iv)phosphoric acid.

For example, in case of a composition comprising a polyvinyl butyralresin, phosphoric acid and a borate or polyphosphate compound (namely,the composition free of an organo functional silane) or a compositioncomprising a polyvinyl butyral resin, phosphoric acid and an organofunctional silane (namely, the composition free of a borate compound orpolyphosphate compound), it is substantially impossible to obtain acoating satisfying the primary object of the present invention, namely acoating having a high corrosion resistance.

According to the present invention, a high anticorrosion effect can beobtained by an anticorrosion primer coating composition comprising apolyvinyl butyral resin, an organo functional silane, at least onemember selected from borate compounds and polyphosphate compounds andphosphoric acid, which may further comprise a phenolic resin and/or ametal powder according to need.

In the coating composition of the present invention, a polyvinyl butyralresin, an organo functional silane and a borate compound and/or apolyphosphate compound are mixed and ground with a solvent customarilyused for a wash primer, for example, an alcohol optionally with anotherpigment, such as an extender pigment or color pigment and othercompatible resin or additive and further optionally with a phenolicresin and/or a metal powder to form a main composition, and the thusformed main composition is mixed with a separately prepared solution ofphosphoric acid when the coating composition is actually applied.

The thus formed coating composition of the present invention is appliedto a substrate to be coated, such as iron, aluminum or zinc plate or thelike, according to a customary coating method.

The resulting coating formed by application of the above coatingcomposition is tightly and closely bonded to the metal substrate by thesynergistic effect of the borate compound and/or polyphosphate compoundand the organo functional silane and therefore, a coating excellent incorrosion resistance can be obtained.

When the anticorrosion primer coating composition of the presentinvention comprising a polyvinyl butyral resin, a borate compound and/ora polyphosphate compound, phosphoric acid and an organo functionalsilane optionally with a metal powder is used as a wash primer of theetching type, or when the anticorrosion primer coating composition ofthe present invention comprising a polyvinyl butyral resin, phosphoricacid, a borate compound and/or polyphosphate compound, an organofunctional silane and a phenolic resin optional with a metal powder isused as a wash primer of the high exposure resistance type, a coatingexcellent in corrosion resistance, weldability, adaptability to weldcutting, adaptability to electroprint marking process andover-coatability can be obtained. Further, the anticorrosion primercoating composition of the present invention is a chromium-free coatingcomposition causing no environmental pollution and having no harmfulinfluence on the health of workers. Accordingly, the anticorrosionprimer coating composition of the present invention is industriallyvaluable as a shop primer.

The present invention will now be described in detail by reference tothe following Examples, in which all of "parts" and "%" are by weight.

EXAMPLE 1

    ______________________________________                                        Main Composition                                                              Ingredients                Parts                                              ______________________________________                                        Phenolic resin (Hitanol 4020 manu-                                                                       11.0                                               factured by Hitachi Chemical Co.                                              Ltd.)                                                                         Polyvinyl butyral resin (S-LEC BM-2                                                                      9.0                                                manufactured by Sekisui Chemical Co.                                          Ltd.)                                                                         Organo functional silane (KBM 303.sup.1)                                                                 0.5                                                manufactured by Shinetsu Silicone                                             Co., Ltd.)                                                                    Yellow iron oxide (Mapico Yellow)                                                                        3.0                                                Phthalocyanine Blue        0.3                                                Carbon black               0.3                                                Aluminum polyphosphate.sup.2)                                                                            2.5                                                Talc                       5.9                                                Barium borate.sup.3)       2.5                                                Suspending agent (organic bentonite)                                                                     1.0                                                Butyl alcohol              11.0                                               Isopropyl alcohol          25.0                                               Toluol                     30.0                                               Total                      100.0                                              ______________________________________                                        Additive                                                                      Ingredients                Parts                                              ______________________________________                                        85% Aqueous solution of phosphoric                                                                       9.0                                                acid                                                                          Water                      5.0                                                Isopropyl alcohol          86.0                                               Total                      100.0                                              ______________________________________                                         Notes-                                                                        .sup.1) KBM 303:                                                              .sup.2) Product manufactured and sold under the tradename "K-82" by           Teikoku Kako Co., Ltd.                                                        .sup.3) Barium metaborate manufactured and sold under the tradename "Busa     11-M1" by Buckman Laboratories Co.                                       

The ingredients of the main composition were kneaded and groundovernight, and 80 parts of the main composition was mixed with 20 partsof the additive to form a coating composition of the present invention.

The thus formed coating composition was applied to a steel plate bymeans of an air spray so that the thickness of the coating was 20μ, andthe coating was dried in a room maintained at a temperature of 20° C anda relative humidity of 75% for 3 days and was then subjected tocomparison tests to obtain the results shown in Table 4.

EXAMPLES 2 to 12

A main composition comprising the ingredients shown in Table 1 waskneaded and ground in the same manner as described in Example 1, and 85parts of the main composition was mixed with 15 parts of the sameadditive as used in Example 1. The resulting composition was applied,dried and subjected to comparison tests in the same manner as describedin Example 1.

Each of the thus obtained coatings was as excellent as the coatingobtained in Example 1 with respect to results of the salt spray test,the outdoor exposure test and the over-coatability test.

                  Table 1                                                         ______________________________________                                        Amounts (parts) of Ingredients in Main Composition                            Ingredients      Example 2   Example 3                                        ______________________________________                                        Phenolic resin   8.0         9.0                                              Polyvinyl butyral resin                                                                        9.0         9.0                                              Organo functional silane                                                                       0.3.sup.1)  1.0.sup.2)                                       Yellow iron oxide                                                                              3.0         3.0                                              Carbon black     0.3         0.3                                              Phthalocyanine Blue                                                                            0.3         0.3                                              Borate compound  5.0.sup.5)  15.0.sup.6)                                      Polyphosphate compound                                                                         5.0.sup.8)  5.0.sup.9)                                       Suspending agent 1.0         1.0                                              Talc             --          --                                               Butyl alcohol    11.0        11.0                                             Isopropyl alcohol                                                                              28.2        25.0                                             Toluol           28.9        20.4                                             Total            100.0       100.0                                            Ingredients      Example 4   Example 5                                        ______________________________________                                        Phenolic resin   7.0         11.0                                             Polyvinyl butyral resin                                                                        9.0         9.0                                              Organo functional silane                                                                       1.3.sup.3)  0.5.sup.4)                                       Yellow iron oxide                                                                              3.0         3.0                                              Carbon black     0.3         0.3                                              Phthalocyanine Blue                                                                            0.3         0.3                                              Borate compound  10.0.sup.7) --                                               Polyphosphate compound                                                                         10.0.sup.10)                                                                              5.0.sup.8)                                       Suspending agent 1.0         1.0                                              Talc             --          3.0                                              Butyl alcohol    11.0        11.0                                             Isopropyl alcohol                                                                              25.0        25.0                                             Toluol           22.1        30.0                                             Total            100.0       100.0                                            Ingredient       Example 6   Example 7                                        ______________________________________                                        Phenolic resin   8.0         9.0                                              Polyvinyl butyral resin                                                                        9.0         9.0                                              Organo functional silane                                                                       0.3.sup.1)  1.0.sup.2)                                       Yellow iron oxide                                                                              3.0         3.0                                              Carbon black     0.3         0.3                                              Phthalocyanine Blue                                                                            0.3         0.3                                              Borate compound  --          --                                               Polyphosphate compound                                                                         10.0.sup.9) 20.0.sup.8)                                      Suspending agent 1.0         1.0                                              Talc             --          --                                               Butyl alcohol    11.0        11.0                                             Isopropyl alcohol                                                                              28.2        25.0                                             Toluol           28.9        20.4                                             Total            100.0       100.0                                            Ingredient       Example 8   Example 9                                        ______________________________________                                        Phenolic resin   7.0         11.0                                             Polyvinyl butyral resin                                                                        9.0         9.0                                              Organo functional silane                                                                       1.3.sup.3)  0.5.sup.4)                                       Yellow iron oxide                                                                              3.0         3.0                                              Carbon black     0.3         0.3                                              Phthalocyanine Blue                                                                            0.3         0.3                                              Borate compound  --          5.0.sup.7)                                       Polyphosphate compound                                                                         20.0.sup.11)                                                                              --                                               Suspending agent 1.0         1.0                                              Talc             --          3.9                                              Butyl alcohol    11.0        11.0                                             Isopropyl alcohol                                                                              25.0        25.0                                             Toluol           22.1        30.0                                             Total            100.0       100.0                                                           Example   Example   Example                                    Ingredient     10        11        12                                         ______________________________________                                        Phenolic resin 8.0       9.0       7.0                                        Polyvinyl butyral                                                                            9.0       9.0       9.0                                        resin                                                                         Organo functional                                                                            0.3.sup.1)                                                                              1.0.sup.2)                                                                              1.3.sup.3)                                 silane                                                                        Yellow iron oxide                                                                            3.0       3.0       3.0                                        Carbon black   0.3       0.3       0.3                                        Phthalocyanine Blue                                                                          0.3       0.3       0.3                                        Borate compound                                                                              10.0.sup.7)                                                                             20.0.sup.5)                                                                             20.0.sup.6)                                Polyphosphate  --        --        --                                         compound                                                                      Suspending agent                                                                             1.0       1.0       1.0                                        Talc           --        --        --                                         Butyl alcohol  11.0      11.0      11.0                                       Isopropyl alcohol                                                                            28.2      25.0      25.0                                       Toluol         28.9      20.4      22.1                                       Total          100.0     100.0     100.0                                      ______________________________________                                         Notes                                                                         .sup.1) γ-Glycidoxypropyltrimethoxysilane manufactured and sold         under the tradename "KBM 403" by Shinetsu Silicone Co., Ltd.                  .sup.2) γ-Methacryloxypropyltrimethoxysilane manufactured and sold      under the tradename "KBM 503" by Shinetsu Silicon Co., Ltd.                   .sup.3) Mixture of equal amounts of KBM 303 and KBM 403 mentioned above       .sup.4) KBM 303 mentioned above                                               .sup.5) Zinc borate (2ZnO · 3B.sub.2 O.sub.3 · 3            · 5H.sub.2 O)                                                        .sup.6) Mixture of equal amounts of barium borate (BaB.sub.2 O.sub.4          · H.sub.2 O) and zinc borate                                         .sup.7) Barium metaborate                                                     .sup.8) Aluminum Polyphosphate (same as used in Example 1)                    .sup.9) Zinc polyphosphate formed by mixing zinc oxide (ZnO) with 85%         phosphoric acid so that the P.sub.2 O.sub.5 /ZnO mole ratio was 3.5,          gradually heating the resulting starting mixture in a porcelain crucible      under agitation so that the temperature was elevated to 250° C ove     a period of 2 hours, heating the mixture for 4 hours in an electric           furnace maintained at 400° C, cooling the heated product and then      pulverizing it                                                                .sup.10) Zinc polyphosphate mentioned above                                   .sup.11) Mixture containing the above-mentioned aluminum polyphosphate an     zinc polyphosphate at a mixing weight ratio of 1:1                       

EXAMPLE 13

    ______________________________________                                        Main Composition                                                              Ingredients                Parts                                              ______________________________________                                        Polyvinyl butyral resin    9.0                                                Organo functional silane   0.5                                                (KBM 303 mentioned above)                                                     Barium metaborate          2.5                                                Aluminum polyphosphate     2.5                                                (same as used in Example 1)                                                   Talc                       5.0                                                Isopropyl alcohol          60.5                                               Butyl alcohol              20.0                                               Total                      100.0                                              ______________________________________                                        Additive                                                                      Ingredients                Parts                                              ______________________________________                                        85% aqueous solution of    18.0                                               phosphoric acid                                                               Water                      16.0                                               Isopropyl alcohol          66.0                                               Total                      100.0                                              ______________________________________                                    

The ingredients of the main composition were kneaded and ground in a potmill overnight, and 80 parts of the main composition was mixed with 20parts of the additive to obtain a coating composition of the presentinvention. In the same manner as described in Example 1, the resultingcoating composition was applied, dried and subjected to comparison teststo obtain the results shown in Table 4.

EXAMPLES 14 to 24

A main composition comprising the ingredients shown in Table 2 waskneaded and ground, and 85 parts of the main composition was mixed with15 parts of the same additive as used in Example 13 to obtain a coatingcomposition. The coating composition was coated, dried and subjected tocomparison tests. It was found that each of the resulting coatingsshowed as excellent results in the salt spray test and overcoatabilitytest as were shown by the coating obtained in Example 13.

                                      Table 2                                     __________________________________________________________________________    Amounts (parts) of Ingredients in Main Composition                                 Polyvinyl                                                                           Organo      Poly-                                                  Example                                                                            Butyral                                                                             Functional                                                                          Borate                                                                              phosphate                                                                           Isopropyl                                                                           Butyl                                      No.  Resin Silane                                                                              Compound                                                                            Compound                                                                            Alcohol                                                                             Alcohol                                                                            Talc                                                                             Total                              __________________________________________________________________________    14   9.0   0.3.sup.1)                                                                          2.5.sup.5)                                                                          2.5.sup.9)                                                                          60.5  20.2 5.0                                                                              100.0                              15   9.0   1.0.sup.2)                                                                          5.0.sup.6)                                                                          5.0.sup.10)                                                                         60.5  19.5 -- 100.0                              16   9.0   1.3.sup.3)                                                                          5.0.sup.7)                                                                          5.0.sup.11)                                                                         60.5  19.2 -- 100.0                              17   9.0   0.5.sup.4)                                                                          --    5.0.sup.9)                                                                          60.5  20.0 -- 100.0                              18   9.0   0.3.sup.1)                                                                          --    10.0.sup.9)                                                                         60.5  20.2 -- 100.0                              19   9.0   1.0.sup.2)                                                                          --    5.0.sup.11)                                                                         60.5  19.5 5.0                                                                              100.0                              20   9.0   1.3.sup.3)                                                                          --    10.0.sup.10)                                                                        60.5  19.2 -- 100.0                              21   9.0   0.5.sup.4)                                                                          5.0.sup.6)                                                                          --    60.5  20.0 5.0                                                                              100.0                              22   9.0   0.3.sup.1)                                                                          10.0.sup.6)                                                                         --    60.5  20.2 -- 100.0                              23   9.0   1.0.sup.2)                                                                          5.0.sup.7)                                                                          --    60.5  19.5 5.0                                                                              100.0                              24   9.0   1.3.sup.3)                                                                          10.0.sup.8)                                                                         --    60.5  19.2 -- 100.0                              __________________________________________________________________________     Notes                                                                         .sup. 1) KBM 403 mentioned above                                              .sup.2) KBM 503 mentioned above                                               .sup.3) Mixture of KBM 303 and KBM 503 mentioned above (mixing weight         ratio = 1:2)                                                                  .sup.4) KBM 303 mentioned above                                               .sup.5) Zinc borate mentioned above                                           .sup.6) Barium metaborate mentioned above                                     .sup.7) Zinc borate mentioned above                                           .sup.8) Mixture of barium metaborate and zinc borate mentioned above          (mixing weight ratio = 1:2)                                                   .sup.9) Aluminum polyphosphate mentioned above                                .sup.10) Zinc polyphosphate mentioned above                                   .sup.11) Calcium polyphosphate prepared from a mixture of calcium oxide       and 85% phosphoric acid (P.sub.2 O.sub.5 /CaO mole ratio = 4) according t     the same method as adopted in Example 3 for preparation of zinc               polyphosphate                                                            

COMPARATIVE EXAMPLES 1 TO 8

Ingredients of a main composition indicated in Table 3 were kneaded andground, and 80 parts of the resulting main composition was mixed with 20parts of an additive indicated in Table 3. In the same manner asdescribed in Example 1, the resulting composition was applied, dried andtested to obtain the results shown in Table 4.

                  Table 3                                                         ______________________________________                                        Amounts (parts) of Ingredients of                                             Main Composition and Additive                                                                  Comparative Comparative                                      Ingredients      Example 1   Example 2                                        ______________________________________                                        Main Composition                                                              Phenolic resin   11.0        11.0                                             Polyvinyl butyral resin                                                                        9.0         9.0                                              Yellow iron oxide                                                                              3.0         3.0                                              Carbon black     0.3         0.3                                              Phthalocyanine Blue                                                                            0.3         0.3                                              Zinc chromate    5.0         --                                               Suspending agent 1.0         1.0                                              Barium metaborate                                                                              --          10.0                                             Aluminum polyphosphate                                                                         --          --                                               Zinc molybdate.sup.1)                                                                          --          --                                               Talc             --          --                                               Butyl alcohol    11.0        11.0                                             Isopropyl alcohol                                                                              25.0        25.0                                             Toluol           34.4        29.4                                             Additive                                                                      85% Aqueous solution of                                                                        9.4         9.0                                              phosphoric acid                                                               Chromic anhydride                                                                              0.2         --                                               Water            4.5         5.0                                              Isopropyl alcohol                                                                              85.9        86.0                                                              Comparative Comparative                                      Ingredients      Example 3   Example 4                                        ______________________________________                                        Main Composition                                                              Phenolic resin   11.0        11.0                                             Polyvinyl butyral resin                                                                        9.0         9.0                                              Yellow iron oxide                                                                              3.0         3.0                                              Carbon black     0.3         0.3                                              Phthalocyanine Blue                                                                            0.3         0.3                                              Zinc chromate    --          --                                               Suspending agent 1.0         1.0                                              Barium metaborate                                                                              --          --                                               Aluminum polyphosphate                                                                         10.0        --                                               Zinc molybdate.sup.1)                                                                          --          10.0                                             Talc             --          --                                               Butyl alcohol    11.0        11.0                                             Isopropyl alcohol                                                                              25.0        25.0                                             Toluol           29.4        29.4                                             Additive                                                                      85% Aqueous solution of                                                                        9.0         9.0                                              phosphoric acid                                                               Chromic anhydride                                                                              --          --                                               Water            5.0         5.0                                              Isopropyl alcohol                                                                              86.0        86.0                                                              Comparative Comparative                                      Ingredient       Example 5   Example 6                                        ______________________________________                                        Main Composition                                                              Phenolic resin   --          --                                               Polyvinyl butyral resin                                                                        9.0         9.0                                              Yellow iron oxide                                                                              --          --                                               Carbon black     --          --                                               Phthalocyanine Blue                                                                            --          --                                               Zinc chromate    8.6         --                                               Suspending agent --          --                                               Barium metaborate                                                                              --          10.0                                             Aluminum polyphosphate                                                                         --          --                                               Zinc molybdate.sup.1)                                                                          --          --                                               Talc             1.4         --                                               Butyl alcohol    20.0        20.0                                             Isopropyl alcohol                                                                              61.0        61.0                                             Toluol           --          --                                               Additive                                                                      85% Aqueous solution of                                                                        18.0        18.0                                             phosphoric acid                                                               Chromic anhydride                                                                              --          --                                               Water            16.0        16.0                                             Isopropyl alcohol                                                                              66.0        66.0                                                              Comparative Comparative                                      Ingredient       Example 7   Example 8                                        ______________________________________                                        Main Composition                                                              Phenolic resin   --          --                                               Polyvinyl butyral resin                                                                        9.0         9.0                                              Yellow iron oxide                                                                              --          --                                               Carbon black     --          --                                               Phthalocyanine Blue                                                                            --          --                                               Zinc chromate    --          --                                               Suspending agent --          --                                               Barium metaborate                                                                              --          --                                               Aluminum polyphosphate                                                                         10.0        --                                               Zinc molybdate.sup.1)                                                                          --          10.0                                             Talc             --          --                                               Butyl alcohol    20.0        20.0                                             Isopropyl alcohol                                                                              61.0        61.0                                             Toluol           --          --                                               Additive                                                                      85% Aqueous solution of                                                                        18.0        18.0                                             phosphoric acid                                                               Chromic anhydride                                                                              --          --                                               Water            16.0        16.0                                             Isopropyl alcohol                                                                              66.0        66.0                                             ______________________________________                                         Note:.sup.1) Product manufactured and sold under the tradename "Moly-Whit     212" by Sherwin Williams Chemicals Co., Ltd.                             

COMPARATIVE EXAMPLE 9

A composition comprising the ingredients shown below was kneaded andground in a pot mill and applied to a soft steel plate by means of anair spray so that the thickness of the coating was 20μ, and theresulting coating was dried at a temperature of 20° C and a relativehumidity of 70% and subjected to comparison tests to obtain the resultsshown in Table 4.

    ______________________________________                                        Ingredients                Parts                                              ______________________________________                                        Long-oil alkyd resin       31.0                                               (manufactured and sold under                                                  tradename "Beckosol P-470" by                                                 Japan Reichhold Chemicals Inc.)                                               Barium metaborate          15.0                                               Talc                       30.3                                               Zinc oxide                 1.5                                                Dispersant                 0.2                                                Aluminum stearate          0.3                                                15% Lead naphthenate drier 1.2                                                 5% Manganese naphthenate drier                                                                          0.3                                                 5% Cobalt naphthenate drier                                                                             0.2                                                Xylol                      20.0                                               Total                      100.0                                              ______________________________________                                    

                                      Table 4                                     __________________________________________________________________________    Results of Comparison Tests                                                   Sample Salt Spray Test.sup.1)                                                                  Outdoor Exposure Test.sup.2)                                                              Over-Coatability Test                            Coating                                                                              50 hours                                                                           150 hours                                                                          3 months                                                                            6 months                                                                            (6 months or 7 days)                             __________________________________________________________________________    Example 1                                                                            ⊚                                                                   ⊚                                                                   ⊚                                                                    ⊚                                                                    100/100                                          Example 5                                                                            ⊚                                                                   ⊚                                                                   ⊚                                                                    ⊚                                                                    100/100                                          Example 9                                                                            ⊚                                                                   ⊚                                                                   ⊚                                                                    ⊚                                                                    100/100                                          Example 13                                                                           ⊚                                                                   --   --    --    100/100                                          Example 17                                                                           ⊚                                                                   --   --    --    100/100                                          Example 21                                                                           ⊚                                                                   --   --    --    100/100                                          Comparative                                                                          ⊚                                                                   O    ⊚                                                                    O     100/100                                          Example 1                                                                     Comparative                                                                          .increment.                                                                        X    .increment.                                                                         X     measurement impossible                           Example 2                    because of extreme                                                            rusting                                          Comparative                                                                          .increment.                                                                        X    .increment.                                                                         X     "                                                Example 3                                                                     Comparative                                                                          .increment.                                                                        X    .increment.                                                                         X     "                                                Example 4                                                                     Comparative                                                                          O ⊚                                                                 --   --    --    100/100                                          Example 5                                                                     Comparative                                                                          X    --   --    --    100/100                                          Example 6                                                                     Comparative                                                                          X    --   --    --    100/100                                          Example 7                                                                     Comparative                                                                          X    --   --    --    100/100                                          Example 8                                                                     Comparative                                                                          .increment.                                                                        X    O     X      90/100                                          Example 9                                                                     __________________________________________________________________________     Notes                                                                         .sup.1) The salt spray test was conducted by using a 5% aqueous solution      of NaCl. The test results were evaluated according to the scale indicated     below.                                                                        .sup.2) The outdoor exposure test results were evaluated according to the     scale indicated below.                                                        .sup.3) A chlorinated rubber type paint was used as an overcoat paint and     the adhesion to the overcoating was evaluated according to the cross-cut      adhesion test (the number of cut sections left after the test) conducted      after 6 months' outdoor exposure in case of wash primers of the high          exposure resistance type or after 7 days' drying in a room in case of was     primers of the etching type.                                             

In each of the salt spray test and outdoor exposure tests, the corrosionresistance was evaluated according to the following scale:

: not changed

0 : slight rusting and blistering

.increment. : rusting and blistering on 10 to 50% of the total area

X : rusting and blistering on substantially entire area

From the foregoing test results, it will readily be understood thatcoating compositions of the high exposure resistance type according tothe present invention (Examples 1, 5 and 9) comprising a polyvinylbutyral resin, a phenolic resin, an organo functional silane, phosphoricacid and a polyphosphate compound and/or a borate compound are farsuperior to the conventional wash primer of the high exposure resistancetype (Comparative Example 1) with respect to the long lasting corrosionresistance. Further, since these coating compositions of the presentinvention are free of chromium and cause no environmental pollution,they are far superior to the conventional wash primer with respect tooperation safety, health maintenance and pollution-preventing effect.Moreover, in view of the ingredients constituting the coatingcompositions of the present invention, it will be apparent that they aremuch improved over the conventional zinc-rich paint with respect toweldability and adaptability to weld cutting.

Chromium-free paints formed by replacing a zinc chromate pigment byother corrosion-resistant pigment in the conventional wash primer of thehigh exposure resistance type (Comparative Examples 2 to 4) have nopractical utility because they are much inferior to the conventionalwash primer with respect to corrosion resistance.

It will also be apparent that coating compositions of the etching typeaccording to the present invention (Examples 13, 17 and 21) comprising apolyvinyl butyral resin, an organo functional silane, phosphoric acidand a polyphosphate compound and/or a borate compound are superior tothe conventional wash primer of the etching type (Comparative Example5), the composition including a borate compound alone and being free ofan organo functional silane (Comparative Example 6), and the compositionincluding a polyphosphate alone and being free of an organo functionalsilane (Comparative Example 7) with respect to corrosion resistance,operation safety and pollution-preventing effect. Moreover, they aresuperior to the known coating composition comprising a borate compoundwith respect to the corrosion resistance.

EXAMPLE 25

    ______________________________________                                        Main Composition                                                              Ingredients                Parts                                              ______________________________________                                        Phenolic resin (Hitanol 4020                                                                             11.0                                               mentioned above)                                                              Polyvinyl butyral resin (S-LEC                                                                           9.0                                                BM-2 mentioned above)                                                         Organo functional silane (KBM 303                                                                        0.5                                                mentioned above)                                                              Yellow iron oxide (Mapico Yellow)                                                                        3.0                                                Carbon black               0.3                                                Phthalocyanine Blue        0.3                                                Barium borate (Busan 11-M1)                                                                              2.5                                                Aluminum polyphosphate (K-82)                                                                            2.5                                                Talc                       1.0                                                Aluminum powder paste (solid                                                                             5.0                                                content = 64%; mineral terpene                                                solution; product manufactured                                                and sold under tradename                                                      "Alpaste 1100N" by Toyo Aluminum                                              Co., Ltd.)                                                                    Suspending agent (organic bentonite)                                                                     1.0                                                Butyl alcohol              11.0                                               Isopropyl alcohol          22.9                                               Toluol                     30.0                                               Total                      100.0                                              Additive                                                                      Ingredients                Parts                                              ______________________________________                                        85% Aqueous solution of    9.0                                                phosphoric acid                                                               Water                      5.0                                                Isopropyl alcohol          86.0                                               Total                      100.0                                              ______________________________________                                    

Ingredients of the main composition except the aluminum powder pastewere kneaded and ground overnight, and the prescribed amount of thealuminum powder paste was added to the kneaded mixture and uniformlydispersed therein to form the main composition. Then, 80 parts of thethus formed main composition was mixed with 20 parts of the additive toform a coating composition of the present invention.

The thus formed coating composition was applied to a steel plate bymeans of an air spray so that the thickness of the resulting coating was20μ and was dried in a room maintained at a temperature of 20° C and arelative humidity of 75% for 3 days. The resulting coating was subjectedto comparison tests to obtain the results shown in Table 8.

Electroprint marking was carried out in the following manner:

A mixture comprising 10 parts of a silicone resin (50% solution in amixed solvent of xylol and toluol), 10 parts of a vinyl acetate resin(50% solution in a mixed solvent of xylol and toluol), 50 parts of zincoxide, 20 parts of xylol and 10 parts of ethyl acetate was blended anddispersed in a ball mill, and the resulting dispersion was heated, driedand pulverized to obtain a photoconductive powder having an averageparticle size of 20μ.

The thus prepared photoconductive powder was uniformly scattered on asteel plate coated with the above-mentioned coating composition by anelectrostatic powder coating machine, and the coated steel plate wasexposed to rays projected from a xenon lamp through a positive originalto form an electrostatic latent image. The photoconductive powder onexposed areas was selectively removed and recovered by application ofpneumatic pressure to obtain a marked visible image. Then, the image wasfixed by heating at 130° C for 30 minutes.

EXAMPLES 26 TO 36

Ingredients of a main composition indicated in Table 5 were kneaded andground in the same manner as described in Example 25 and 85 parts of theresulting main composition was mixed with 15 parts of the same additiveas used in Example 25. The resulting composition was applied, dried andtested in the same manner as described in Example 25.

It was found that each of the thus prepared compositions was asexcellent in corrosion resistance of the coating and adaptability to theelectroprint marking process as the coating composition obtained inExample 25.

                  Table 5                                                         ______________________________________                                        Amounts (parts) of Ingredients in Main Composition                                             Example  Example  Example                                    Ingredients      26       27       28                                         ______________________________________                                        Phenolic resin   8.0      9.0      7.0                                        Polyvinyl butyral resin                                                                        9.0      9.0      9.0                                        Organo functional silane                                                                       0.3.sup.1)                                                                             1.0.sup.2)                                                                             1.3.sup.3)                                 Yellow iron oxide                                                                              3.0      3.0      3.0                                        Carbon black     0.3      0.3      0.3                                        Phthalocyanine Blue                                                                            0.3      0.3      0.3                                        Borate compound  5.0.sup.5)                                                                             15.0.sup.6)                                                                            10.0.sup.7)                                Polyphosphate compound                                                                         5.0.sup.8)                                                                             5.0.sup.9)                                                                             10.0.sup.9)                                Aluminum powder paste.sup.11)                                                                  5.0      3.0      7.0                                        Suspending agent 1.0      1.0      1.0                                        Talc             --       --       --                                         Butyl alcohol    11.0     11.0     11.0                                       Isopropyl alcohol                                                                              23.2     22.0     18.0                                       Toluol           28.9     20.4     22.1                                       Total            100.0    100.0    100.0                                                       Example  Example  Example                                    Ingredients      29       30       31                                         ______________________________________                                        Phenolic resin   11.0     8.0      9.0                                        Polyvinyl butyral resin                                                                        9.0      9.0      9.0                                        Organo functional silane                                                                       0.5.sup.4)                                                                             0.3.sup.1)                                                                             1.0.sup.2)                                 Yellow iron oxide                                                                              3.0      3.0      0.3                                        Carbon black     0.3      0.3      0.3                                        Phthalocyanine Blue                                                                            0.3      0.3      0.3                                        Borate compound  5.0.sup.7)                                                                             10.0.sup.7)                                                                            20.0.sup.5)                                Polyphosphate compound                                                                         --       --       --                                         Aluminum powder paste.sup.11)                                                                  5.0      6.0      4.0                                        Suspending agent 1.0      1.0      1.0                                        Talc             3.9      --       --                                         Butyl alcohol    11.0     11.0     11.0                                       Isopropyl alcohol                                                                              25.0     22.2     21.0                                       Toluol           30.0     28.9     23.1                                       Total            100.0    100.0    100.0                                                       Example  Example  Example                                    Ingredients      32       33       34                                         ______________________________________                                        Phenolic resin   7.0      11.0     8.0                                        Polyvinyl butyral resin                                                                        9.0      9.0      9.0                                        Organo functional silane                                                                       1.3.sup.3)                                                                             0.5.sup.4)                                                                             0.3.sup.1)                                 Yellow iron oxide                                                                              3.0      3.0      3.0                                        Carbon black     0.3      0.3      0.3                                        Phthalocyanine Blue                                                                            0.3      0.3      0.3                                        Borate compound  20.0.sup.6)                                                                            --       --                                         Polyphosphate compound                                                                         --       5.0.sup.8)                                                                             10.0.sup.9)                                Aluminum powder paste.sup.11)                                                                  7.0      5.0      5.0                                        Suspending agent 1.0      1.0      1.0                                        Talc             --       3.9      --                                         Butyl alcohol    11.0     11.0     11.0                                       Isopropyl alcohol                                                                              18.0     20.0     23.2                                       Toluol           22.1     30.0     28.9                                       Total            100.0    100.0    100.0                                      Ingredients      Example 35  Example 36                                       ______________________________________                                        Phenolic resin   9.0         7.0                                              Polyvinyl butyral resin                                                                        9.0         9.0                                              Organo functional silane                                                                       1.0.sup.2)  1.3.sup.3)                                       Yellow iron oxide                                                                              3.0         3.0                                              Carbon black     0.3         0.3                                              Phthalocyanine Blue                                                                            0.3         0.3                                              Borate compound  --          --                                               Polyphosphate compound                                                                         20.0.sup.8) 20.0.sup.10)                                     Aluminum powder paste.sup.11)                                                                  3.0         7.0                                              Suspending agent 1.0         1.0                                              Talc             --          --                                               Butyl alcohol    11.0        11.0                                             Isopropyl alcohol                                                                              22.0        18.0                                             Toluol           20.4        22.1                                             Total            100.0       100.0                                            ______________________________________                                         Notes                                                                         .sup.1) KBM 403 mentioned above                                               .sup.2) KBM 503 mentioned above                                               .sup.3) Mixture of equal amounts of KBM 303 and KBM 403 mentioned above       .sup.4) KBM 303 mentioned above                                               .sup.5) Zinc borate (2ZnO · 3B.sub.2 O.sub.3 · 3            · 5H.sub.2 O)                                                        .sup.6) Mixture of equal amounts of barium borate (BaB.sub.2 O.sub.4          · H.sub.2 O) and zinc borate                                         .sup.7) Barium borate (BaB.sub.2 O.sub.4 · H.sub.2 O)                .sup.8) Aluminum polyphosphate (same as used in Example 1)                    .sup.9) Zinc polyphosphate (same as used in Example 3)                        .sup.10) Mixture of aluminum polyphosphate and zinc polyphosphate (mixing     weight ratio = 1:1)                                                           .sup.11) Product manufactured and sold under tradename "Alpaste 1700 NL"      by Toyo Aluminum Co., Ltd. (solid content = 64%; mineral terpene solution                                                                              

EXAMPLE 37

    ______________________________________                                        Main Composition                                                              Ingredients                Parts                                              ______________________________________                                        Polyvinyl butyral resin    9.0                                                Organo functional silane   0.5                                                (KBM 303 mentioned above)                                                     Barium borate              2.5                                                Aluminum polyphosphate (same as                                                                          2.5                                                used in Example 25)                                                           Talc                       5.0                                                Aluminum alloy powder paste                                                                              5.0                                                (aluminum/zinc weight ratio =                                                 95/5; solid content = 64%;                                                    mineral terpene solution                                                      Isopropyl alcohol          55.0                                               Butyl alcohol              20.0                                               Total                      100.0                                              ______________________________________                                        Additive                                                                      Ingredients                Parts                                              ______________________________________                                        85% Aqueous solution of phosphoric                                                                       18.0                                               acid                                                                          Water                      16.0                                               Isopropyl alcohol          66.0                                               Total                      100.0                                              ______________________________________                                    

The ingredients of the main composition were kneaded and ground in thesame manner as in Example 25, and 80 parts of the resulting maincomposition was mixed with 20 parts of the additive to obtain a coatingcomposition of the present invention. The coating composition wasapplied, dried and tested in the same manner as in Example 25 to obtainresults shown in Table 8.

EXAMPLES 38 to 48

Ingredients of a main composition indicated in Table 6 were kneaded andground, and 85 parts of the resulting main composition were mixed with15 parts of the same additive as used in Example 37. The resultingcompositions were subjected to comparison tests in the same manner asdescribed in Example 25. It was found that each coating composition wasas excellent as the coating composition obtained in Example 37 withrespect to corrosion resistance of the resulting coating andadaptability to the electroprint marking process.

                                      Table 6                                     __________________________________________________________________________    Amounts (parts) of Ingredients in Main Composition                                 Polyvinyl                                                                           Organo      Polyphos-           Aluminum                           Example                                                                            Butyral                                                                             Functional                                                                          Borate                                                                              phate Isopropyl                                                                           Butyl   Powder                             No.  Resin Silane                                                                              Compound                                                                            Compound                                                                            Alcohol                                                                             Alcohol                                                                            Talc                                                                             Paste Total                        __________________________________________________________________________    38   9.0   0.3.sup.1)                                                                          2.5.sup.5)                                                                          2.5.sup.6)                                                                          56.5  20.2 5.0                                                                              4.0.sup.11)                                                                         100.0                        39   9.0   1.0.sup.2)                                                                          5.0.sup.6)                                                                          5.0.sup.9                                                                           53.5  19.5 -- 7.0.sup.11)                                                                         100.0                        40   9.0   1.3.sup.3)                                                                          5.0.sup.5)                                                                          5.0.sup.10)                                                                         55.5  19.2 -- 5.0.sup.11)                                                                         100.0                        41   9.0   0.5.sup.4)                                                                          5.0.sup.6)                                                                          --    55.5  20.0 5.0                                                                              5.0.sup.12)                                                                         100.0                        42   9.0   0.3.sup.1)                                                                          10.0.sup.6)                                                                         --    52.5  20.2 -- 8.0.sup.11)                                                                         100.0                        43   9.0   1.0.sup.2)                                                                          5.0.sup.5)                                                                          --    54.5  19.5 5.0                                                                              6.0.sup.11)                                                                         100.0                        44   9.0   1.3.sup.3)                                                                          10.0.sup.7)                                                                         --    57.5  19.2 -- 3.0.sup.11)                                                                         100.0                        45   9.0   0.5.sup.4)                                                                          --    5.0 8)                                                                              55.5  20.0 5.0                                                                              5.0.sup.12)                                                                         100.0                        46   9.0   0.3.sup.1)                                                                          --    10.0.sup.8)                                                                         56.5  20.2 -- 4.0.sup.11)                                                                         100.0                        47   9.0   1.0.sup.2)                                                                          --    5.0.sup. 10)                                                                        54.5  19.5 5.0                                                                              6.0.sup.11)                                                                         100.0                        48   9.0   1.3.sup.3)                                                                          --    10.0.sup.9)                                                                         55.5  19.2 -- 5.0.sup.11)                                                                         100.0                        __________________________________________________________________________     Notes                                                                         .sup.1) KBM 403 mentioned above                                               .sup.2) KBM 503 mentioned above                                               .sup.3) Mixture of KBM 303 and KBM 503 mentioned above (mixing weight         ratio = 1:2)                                                                  .sup.4) KBM 303 mentioned above                                               .sup.5) Zinc borate mentioned above                                           .sup.6) Barium metaborate mentioned above                                     .sup.7) Mixture of barium metaborate and zinc borate (mixing weight ratio     = 1:2)                                                                        .sup.8) Aluminum polyphosphate same as used in Example 1                      .sup.9) Zinc polyphosphate same as used in Example 3                          .sup.10) Calcium polyphosphate same as used in Example 19                     .sup.11) Alpaste 1100 N mentioned above                                       .sup.12) Aluminum alloy powder paste same as used in Example 37          

COMPARATIVE EXAMPLES 10 to 17

Ingredients of a main composition indicated in Table 7 were kneaded andground in the same manner as described in Example 37, and 80 parts ofthe thus formed main composition were mixed with 20 parts of an additiveindicated in Table 7 to form a coating composition. The resultingcoating composition was tested in the same manner as described inExample 37 to obtain the results shown in Table 8.

                  Table 7                                                         ______________________________________                                        Amounts (parts) of Ingredients of                                             Main Composition and Additive                                                                  Comparative Comparative                                      Ingredients      Example 10  Example 11                                       ______________________________________                                        Main Composition                                                              Phenolic resin   11.0        11.0                                             Polyvinyl butyral resin                                                                        9.0         9.0                                              Yellow iron oxide                                                                              3.0         3.0                                              Carbon black     0.3         0.3                                              Phthalocyanine Blue                                                                            0.3         0.3                                              Zinc chromate    5.0         --                                               Suspending agent 1.0         1.0                                              Barium metaborate                                                                              --          10.0                                             Aluminum polyphosphate                                                                         --          --                                               Zinc molybdate.sup.1)                                                                          --          --                                               Aluminum powder paste.sup.2)                                                                   5.0         5.0                                              Talc             --          --                                               Butyl alcohol    11.0        11.0                                             Isopropyl alcohol                                                                              20.0        20.0                                             Toluol           34.4        29.4                                             Additive                                                                      85% Aqueous solution                                                                           9.4         9.0                                              of phosphoric acid                                                            Chromic anhydride                                                                              0.2         --                                               Water            4.5         5.0                                              Isopropyl alcohol                                                                              85.9        86.0                                                              Comparative Comparative                                      Ingredients      Example 12  Example 13                                       ______________________________________                                        Main Composition                                                              Phenolic resin   11.0        11.0                                             Polyvinyl butyral resin                                                                        9.0         9.0                                              Yellow iron oxide                                                                              3.0         3.0                                              Carbon black     0.3         0.3                                              Phthalocyanine Blue                                                                            0.3         0.3                                              Zinc chromate    --          --                                               Suspending agent 1.0         1.0                                              Barium metaborate                                                                              --          --                                               Aluminum polyphosphate                                                                         10.0        --                                               Zinc molybdate.sup.1)                                                                          --          10.0                                             Aluminum powder paste.sup. 2)                                                                  5.0         --                                               Talc             --          --                                               Butyl alcohol    11.0        11.0                                             Isopropyl alcohol                                                                              20.0        25.0                                             Toluol           29.4        29.4                                             Additive                                                                      85% Aqueous solution                                                                           9.0         9.0                                              of phosphoric acid                                                            Chromic anhydride                                                                              --          --                                               Water            5.0         5.0                                              Isopropyl alcohol                                                                              86.0        86.0                                                              Comparative Comparative                                      Ingredients      Example 14  Example 15                                       ______________________________________                                        Main Composition                                                              Phenolic resin   --          --                                               Polyvinyl butyral resin                                                                        9.0         9.0                                              Yellow iron oxide                                                                              --          --                                               Carbon black     --          --                                               Phthalocyanine Blue                                                                            --          --                                               Zinc chromate    8.6         --                                               Suspending agent --          --                                               Barium metaborate                                                                              --          10.0                                             Aluminum polyphosphate                                                                         --          --                                               Zinc molybdate.sup.1)                                                                          --          --                                               Aluminum powder paste.sup.2)                                                                   --          5.0                                              Talc             1.4         --                                               Butyl alcohol    20.0        20.0                                             Isopropyl alcohol                                                                              61.0        56.0                                             Toluol           --          --                                               Additive                                                                      85% Aqueous solution                                                                           18.0        18.0                                             of phosphoric acid                                                            Chromic anhydride                                                                              --          --                                               Water            16.0        16.0                                             Isopropyl alcohol                                                                              66.0        66.0                                                              Comparative Comparative                                      Ingredients      Example 16  Example 17                                       ______________________________________                                        Main Composition                                                              Phenolic resin   --          --                                               Polyvinyl butyral resin                                                                        9.0         9.0                                              Yellow iron oxide                                                                              --          --                                               Carbon black     --          --                                               Phthalocyanine Blue                                                                            --          --                                               Zinc chromate    --          --                                               Suspending agent --          --                                               Barium metaborate                                                                              --          --                                               Aluminum polyphosphate                                                                         10.0        --                                               Zinc molybdate.sup.1)                                                                          --          10.0                                             Aluminum powder paste.sup.2)                                                                   5.0         5.0                                              Talc             --          --                                               Butyl alcohol    20.0        20.0                                             Isopropyl alcohol                                                                              56.0        56.0                                             Toluol           --          --                                               Additive                                                                      85% Aqueous solution                                                                           18.0        18.0                                             of phosphoric acid                                                            Chromic anhydride                                                                              --          --                                               Water            16.0        16.0                                             Isopropyl alcohol                                                                              66.0        66.0                                             ______________________________________                                    

                  Table 8                                                         ______________________________________                                        Test Results                                                                          Salt Spray Test.sup.1)                                                Sample    50         100          200                                         Coating   hours      hours        hours                                       ______________________________________                                        Example 25                                                                              ⊚                                                                         ⊚                                                                           ⊚                            Example 29                                                                              ⊚                                                                         ⊚                                                                           ⊚                            Example 33                                                                              ⊚                                                                         ⊚                                                                           ⊚                            Example 37                                                                              ⊚                                                                         O            --                                          Example 38                                                                              ⊚                                                                         O            --                                          Example 42                                                                              ⊚                                                                         O            --                                          Example 45                                                                              ⊚                                                                         O            --                                          Example 46                                                                              ⊚                                                                         O            --                                          Comparative                                                                             ⊚                                                                         O            X                                           Example 10                                                                    Comparative                                                                             Δ    X            --                                          Example 11                                                                    Comparative                                                                             Δ    X            --                                          Example 12                                                                    Comparative                                                                             Δ    X            --                                          Example 13                                                                    Comparative                                                                             O - ⊚                                                                     X            --                                          Example 14                                                                    Comparative                                                                             X          --           --                                          Example 15                                                                    Comparative                                                                             X          --           --                                          Example 16                                                                    Comparative                                                                             X          --           --                                          Example 17                                                                    Sample    Outdoor Exposure Test.sup.2)                                        Coating   3 months   6 months     9 months                                    ______________________________________                                        Example 25                                                                              ⊚                                                                         ⊚                                                                           ⊚                            Example 29                                                                              ⊚                                                                         ⊚                                                                           ⊚                            Example 33                                                                              ⊚                                                                         ⊚                                                                           ⊚                            Example 37                                                                              --         --           --                                          Example 38                                                                              --         --           --                                          Example 42                                                                              --         --           --                                          Example 45                                                                              --         --           --                                          Example 46                                                                              --         --           --                                          Comparative                                                                             ⊚                                                                         O            X                                           Example 10                                                                    Comparative                                                                             Δ    X            --                                          Example 11                                                                    Comparative                                                                             Δ    X            --                                          Example 12                                                                    Comparative                                                                             Δ    X            --                                          Example 13                                                                    Comparative                                                                             --         --           --                                          Example 14                                                                    Comparative                                                                             --         --           --                                          Example 15                                                                    Comparative                                                                             --         --           --                                          Example 16                                                                    Comparative                                                                             --         --           --                                          Example 17                                                                            Adaptability to Electroprint                                                  Marking Process                                                                            Recovery Loss                                            Sample    Resolution of Photoconduc-                                                                            Sensitivity.sup.5)                          Coating   of Image.sup.3)                                                                          tive Powder.sup.4)                                                                         (seconds)                                   ______________________________________                                        Example 25                                                                              good       below 1%     9                                           Example 29                                                                              good       below 1%     10                                          Example 33                                                                              good       below 1%     8                                           Example 37                                                                              good       below 1%     10                                          Example 38                                                                              good       below 1%     10                                          Example 42                                                                              good       below 1%     9                                           Example 45                                                                              good       below 1%     8                                           Example 46                                                                              good       below 1%     9                                           Comparative                                                                             good       below 1%     10                                          Example 10                                                                    Comparative                                                                             good       below 1%     10                                          Example 11                                                                    Comparative                                                                             good       below 1%     10                                          Example 12                                                                    Comparative                                                                             bad        10%          30                                          Example 13                                                                    Comparative                                                                             bad        10%          30                                          Example 14                                                                    Comparative                                                                             good       below 1%     10                                          Example 15                                                                    Comparative                                                                             good       below 1%     10                                          Example 16                                                                    Comparative                                                                             good       below 1%     10                                          Example 17                                                                    ______________________________________                                         Notes                                                                         .sup.1) The salt spray test was conducted by using 5% aqueous solution of     NaCl. The test results were evaluated according to the scale indicated        below                                                                         .sup.2) The outdoor exposure test results were evaluated according to the     scale indicated below                                                         .sup.3) The resolution of the image was evaluated by naked eye observatio     .sup.4) The recovery loss of the photoconductive powder was calculated        according to the following formula:                                           ##STR3##                                                                      .sup.5) The sensitivity is expressed in terms of the time (seconds) durin     which the sensitivity was attenuated under 60 luxes                      

In each of the salt spray test and outdoor exposure test, the corrosionresistance was evaluated according to the following scale:

: not changed

: slight rusting and blistering

.increment.: rusting and blistering on 10 to 50% of the total area

X: rusting and blistering on substantially entire area

From the test results shown in Table 8, it will readily be understoodthat coating compositions of the high exposure resistance type accordingto the present invention (Examples 25, 29 and 33) comprising a polyvinylbutyral resin, a phenolic resin, an organo functional silane, a boratecompound and/or a polyphosphate compound, a metal powder and phosphoricacid are superior to the conventional wash primer of the high exposureresistance type (Comparative Example 10) with respect to long lastingcorrosion resistance. Further, it is apparent that since these coatingcompositions are chromium-free paints causing no pollution, they are farsuperior to the conventional wash primer of the high exposure resistancetype with respect to operation safety, health maintenance and the effectof preventing environmental pollution. Moreover, it is seen that thesecoating compositions are superior or comparable to the conventional washprimer with respect to adaptability to the electroprint marking process.Still further, in view of the constituents of these coating compositionsaccording to the present invention, it is apparent that they are muchimproved over the conventional zinc-rich paint with respect toweldability.

Chromium-free paints formed by replacing a zinc chromate pigment byother anticorrosion pigment in the conventional wash primer of the highexposure resistance type (Comparative Examples 11 to 13) are muchinferior to the conventional wash primer with respect to corrosionresistance and they have no practical utility at all.

It will also be apparent that coating compositions of the etching typeaccording to the present invention (Examples 37, 38, 42, 45 and 46)comprising a polyvinyl butyral resin, an organo functional silane, aborate compound and/or a polyphosphate compound, a metal powder andphosphoric acid are superior to the conventional wash primer to theetching type (Comparative Example 14), the composition including aborate alone and being free of an organo functional silane (ComparativeExample 15), the composition including a polyphosphate alone and beingfree of an organo functional silane (Comparative Example 16) and thecomposition including zinc molybdate (Comparative Example 17) withrespect to corrosion resistance, operation safety, health maintenance,the effect of preventing environmental pollution and adaptability to theelectroprint marking process.

What is claimed is:
 1. An anticorrosion primer coating compositioncomprising(i) 100 parts by weight of a polyvinyl butyral resin, (ii) 1to 25 parts by weight of at least one organo functional silane selectedfrom the group consisting of aminoalkoxysilane compounds represented bythe following general formula: ##STR4## wherein R¹ stands for a divalenthydrocarbon group having 1 to 4 carbon atoms, R² and R³ represent amonovalent hydrocarbon group having 1 to 4 carbon atoms, Z stands for ahydrogen atom or an aminoalkyl group, and m is 1 or 0, andalkylalkoxysilane compounds represented by the following generalformula: ##STR5## wherein R⁴ stands for a divalent hydrocarbon grouphaving 1 to 4 carbon atoms, R⁵ and R⁶ represent a monovalent hydrocarbongroup having 1 to 4 carbon atoms, Q stands for a methacryloxy, acryloxy,glycidoxy or epoxycyclohexyl group, and n is 1 or
 0. (iii) 20 to 350parts by weight of at least one member selected from the groupconsisting of inorganic borate compounds and polyphosphate compounds and(iv) 5 to 50 parts by weight of phosphoric acid.
 2. An anticorrosionprimer coating composition as set forth in claim 1 wherein the component(iii) is a mixture of a borate compound and a polyphosphate compound inwhich the mixing weight ratio is in the range of from 1/9 to 9/1.
 3. Ananticorrosion primer coating composition as set forth in claim 1 whereinthe component (ii) is at least one member selected from the groupconsisting of β-(3,4-epoxycyclohexyl)-ethyltrimethoxysilane,γ-glycidoxypropyltrimethoxysilane andγ-methacryloxypropyltrimethoxysilane.
 4. An anticorrosion primer coatingcomposition as set forth in claim 1 wherein the borate compound is atleast one member selected from the group consisting of bariummetaborate, zinc borate, sodium tetraborate, barium tetraborate,magnesium metaborate and aluminum orthoborate.
 5. An anticorrosionprimer coating composition as set forth in claim 1 wherein thepolyphosphate compound is at least one member selected from the groupconsisting of aluminum polyphosphate, zinc polyphosphate and calciumpolyphosphate.
 6. An anticorrosion primer coating composition as setforth in claim 1 which further comprises up to 200 parts by weight of aphenolic resin.
 7. An anticorrosion primer coating composition as setforth in claim 6 which further comprises 10 to 130 parts by weight of ametal powder.
 8. An anticorrosion primer coating composition as setforth in claim 7 wherein the metal powder is at least one memberselected from the group consisting of powders of metallic aluminum andaluminum alloys.
 9. An anticorrosion primer coating composition as setforth in claim 1 which further comprises 10 to 130 parts by weight of ametal powder.
 10. An anticorrosion primer coating composition as setforth in claim 9 wherein metal powder is at least one member selectedfrom the group consisting of powders of metallic aluminum and aluminumalloys.